Thin, nearly transparent films of long carbon nanotubes have been produced at Rice University and show promise for flexible electronics.
- A thin film of pure carbon nanotubes produced at Rice University shows promise as a component of flexible, transparent touchscreens.
The researchers say their method is simple and scaleable for industrial use.
A Rice University team has hit upon a method to produce nearly transparent films of electrically conductive carbon nanotubes, a goal sought by researchers around the world.
The lab of Rice researcher Matteo Pasquali found that slides dipped into a solution of pure nanotubes in chlorosulfonic acid (CSA) left them with an even coat of nanotubes that, after further processing, had none of the disadvantages seen with other methods.
The films may be suitable for flexible electronic displays and touchscreens, according to the paper published this month in the American Chemical Society journal ACS Nano.
A frustrating characteristic of nanotubes, particularly long ones, is that they attract each other in common solvents, making it a challenge to disperse them. Long nanotubes are believed to be the key to high-performance films.
Functionalizing nanotubes – dressing them with chemicals – can make them less attractive to each other, but it degrades their desirable electrical properties. Combinations of surfactants and sonication have also been tried, but the nanotubes break during sonication, and the surfactant leaves a residue that cannot be washed away, he said.
These methods, combined with various means of mechanical coating, have been used to create nanotube films, but none with the level of quality achieved by the Pasquali lab. The Rice films which are made of nanotubes thousands of times longer than they are wide, remain electrically stable after more than three months, said graduate student and lead author Francesca Mirri.
Mirri and her colleagues produced films by combining single- or double-walled carbon nanotubes with CSA in various concentrations. They dipped glass slides into the nanotube solutions with a motorized arm to ensure even coating as the slides were steadily withdrawn.
They used chloroform to coagulate the acid and dry the slides, followed by a wash of diethyl ether. The researchers were surprised to find the chloroform did not disrupt the thin liquid layer. The result was a film several nanometers thick that provided the best tradeoff between transparency and sheet resistance, a measure of conductivity.
A thin film of pure carbon nanotubes produced at Rice University shows promise as a component of flexible, transparent touchscreens.
The research was supported by the Air Force Office of Scientific Research, the Air Force Research Laboratories and the Robert A. Welch Foundation.